The invention relates to a variable valve control device for reciprocating engines, internal combustion engines in particular, as specified in the preamble of claim 1.
Such a variable valve control device is disclosed, for example, in DE 42 23 173 A1; it is a device in which an adjustable sliding block (rocker arm) element in the cylinder head of the internal combustion engine, with an inclined adjusting plane and a roller, is introduced between the cam of a camshaft on one side and the cup stem on the shaft end of an upper valve on the other side. Both a full stroke and partial strokes to around zero stroke can be controlled by displacement of the sliding block element relative to the cam. In the case of a full stroke such displacement results in valve actuation which with respect to valve lift and velocity profile development is determined by the geometry of the cam and the inclined adjusting plane and which may be correspondingly optimized. In the case of the partial stroke, of course, first an idle stroke (=excitation movement) is executed and then the partial stroke (=generation movement), a cam area exerting its effect later in time in this instance, an area which of necessity may cause a different velocity profile development or high, jerky valve accelerations. This applies both to valve opening (upward slope) and valve closing (downward slope).
The object of the invention is to create a generic variable valve control device which permits extensive valve stroke changes accompanied by valve actuation as free of jerkiness as possible and which is of rugged design and cost-effective in manufacture.
It is claimed for the invention that this object is attained by the features specified in claim 1. Advantageous developments of the invention are specified in the additional claims.
It is proposed in accordance with the invention that there be inserted between the cam and the valve actuation element, a valve rocker in particular, an empty run (free travel) component which effects preacceleration (excitation movement) of the sliding block in the case both of a full stroke and partial strokes of the upper valve, so that the generation movement (opening movement) of the upper valve is controlled with the positive and negative acceleration desired essentially by the inclined adjusting plane of the rocker arm element. This decoupling of excitation movement and generation movement executed by the geometric design of cam and variable valve control device creates a velocity profile without higher acceleration peaks and accordingly a rugged valve train which is improved from the viewpoint of wear and operating noise, to the greatest extent possible independently of the assigned valve travel.
The layout of the valve train as specified in claim 3 additionally permits longer valve strokes and accordingly a larger valve stroke adjustment range determined by a valve rocker having the associated more favorable rocker ratios and by the positioning of the inclined adjusting plane more or less perpendicular to the axis of rotation of the cam, which results in shorter lateral travel distances of the roll pack especially during excitation movement. In this situation the contact surface of the valve rocker for the roll pack may be oriented parallel to the direction of displacement of the rocker arm element.
In another advantageous embodiment of the invention the inclined adjusting plane of the rocker arm element is in the form of a slotted rocker arm guide whose opposite guide surface forms an inclined preacceleration plane in excitation movement of the sliding block element which provides smooth transition to the inclined contact plane section of the inclined adjusting plane for the movement of generation. This results in gentle sliding positioning of the sliding block element on the valve rocker followed by generation movement without a transitional element.
The sliding block element may advantageously be pretensioned against the cam by means of at least one simple spring clip. The spring clip may preferably be supported on the rocker arm element by one of its sides and acts in conjunction with a second, elongated side on the sliding block element pretensioning the latter against the cam.
In the case of use of a hydraulic valve play equalization element in the valve train in particular it may be advantageous for the valve rocker to rest against a stop of the rocker arm component when the upper valve is in the closed position. The pulley assembly may be lifted by the valve rocker as a result of pretensioning of the spring clip, so that constant contact is established between the sliding block element and the cam, and free play is established between the valve rocker, the rocker arm element, and the valve shaft.
In order to achieve a valve rocker structure which is rigid and produces high layout accuracy, preference is given to mounting the valve rocker in the cylinder head by way of one valve rocker axis. In this situation the hydraulic valve play equalization element could then be mounted on the end of the valve rocker operating in conjunction with the shaft end of the upper valve. It is proposed, however, that preference be given to a valve rocker in at least two parts, one part of which is pivotably mounted, while the other part resembling a rocker rests on one side on the hydraulic valve play equalization element and on the other on the shaft end of the upper valve, the two interposed valve rocker parts being connected to each other in operation (by means of a carrier extending transversely or by a pin joint connection).
One exemplary embodiment of the invention is explained in greater detail in what follows.